Re: linking tables to C++ objects?
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- Subject: Re: linking tables to C++ objects?
- From: Graham Wakefield <lists@...>
- Date: 2007年2月26日 17:36:12 -0800
Thanks.
Wouldn't it be cheaper & more efficient to use the registry rather
than a metatable subtable?
callback(cpp_class *c)
{
lua_State *L = c->lua();
lua_pushlightuserdata(L, c);
lua_gettable(L, LUA_REGISTRYINDEX);
//either nil or your userdata will no be on the stack
}
If I need to type-check, I can compare the metatable of the userdata
to the class name:
bool typecheck(lua_State * L)
{
lua_getfield(L, LUA_REGISTRYINDEX, c::classname);
if (lua_getmetatable(L, -1) && lua_rawequal(L, -1, -2))
{
lua_pop(L, 2); // remove both metatables
return true;
}
lua_pop(L, 1); // remove class table
return false;
}
On Feb 26, 2007, at 5:23 PM, Wesley Smith wrote:
I think, as suggested by Rici, that you need a table mapping C++
pointers to userdata in the Lua userdata's metatable. somehow you'll
need to get the lua_State. In this case, I assume a pointer is cached
in the cpp_class and that the table of cpp pointers to userdata is in
the metatable's "instances" field;
pseudo code
callback(cpp_class *c)
{
lua_State *L = c->lua();
luaL_getmetatable(L, cpp_class::metatable_name);
lua_pushstring(L, "instances");
lua_gettable(L, -2)
lua_pushinteger(L, (int)c);
lua_gettable(L, -2)
//either nil or your userdata will no be on the stack
}
Also I would make the "instances" table a weak table with __mode = "v"
wes